1. Field of the Invention
The present invention generally relates to multi-channel audio surround systems and more specifically relates to discrete multi-channel audio systems combined with multi-channel matrix surround systems.
2. Description of the Related Art
Matrix surround systems have been commonly known and used for approximately thirty years. The work of Peter Scheiber in the late sixty""s and early seventy""s is perhaps the most well known. The basic concept of a matrix system is to expand the number of audio channels available from a two channel stereo recording, or transmission media. Anyone skilled in the art is knowledgeable of the fact that the commonly known xe2x80x9cDolby Stereoxe2x80x9d cinema systems as well as the xe2x80x9cDolby Pro Logicxe2x80x9d consumer systems are based on the original patents issued to Peter Schieber. The Dolby system is referred to as a 4-2-4 matrix system. The obvious requirement of all matrix systems is that a discrete two channel recording or transmission media (Left and Right channels) must be available to allow additional channels to be added as a L+R and or Lxe2x88x92R signal. It is also obvious to the skilled artisan that any existing stereo, or pair of two or more discrete channels of audio, can be enhanced with the use of any of the existing matrix systems. This would include stereo recordings, FM stereo broadcast, cable TV transmission, internet audio and DVD audio to name a few of the countless possible applications. It also becomes obvious to anyone skilled in the art to consider the application of matrix enhancement to any of the discrete multi-channel audio formats such as Dolby Digital (AC-3), DTS (Digital Theater Systems), or the Sony format known as SDDS. The most obvious application would be to enhance the stereo rear or xe2x80x9csurroundxe2x80x9d channels by applying a 4-2-4 matrix system. Anyone skilled in the art quickly realizes that with any of the above mentioned discrete multi-channel systems, any one of the known matrix decoders including Dolby Pro-Logic, can be connected to the left and right surround outputs. The obvious result is that any dominate audio originally mixed equally in both of the surround channels would produce a center surround output from the center output of the Dolby Pro-Logic decoder.
It is also obvious to one skilled in the art that by using the Left and Right front outputs from the matrix decoder for the left and right surround outputs, center surround audio will be subtracted from the left and right output. This would provide the user with a six channel system having a potential benefit for all of the currently available releases in any of the above mentioned discrete multi-channel formats. The above described system can easily be realized, by any consumer, by connecting one of the currently available consumer xe2x80x9cDigital Systemsxe2x80x9d, Dolby Digital or DTS, with one of the available consumer matrix systems. There are several matrix decoding systems that could be used, as is obvious to those skilled in the art. The Dolby Pro-Logic system is used as an example of the most commonly available system. The combined system described above has already been realized in numerous professional cinema application and will illustrate an example of the prior art. A number of professional cinemas have connected one of the commercially available professional discrete digital systems with one of the commercially available professional matrix decoders. The combined system was connected to provide the cinema system with a center surround channel. As previously mentioned a center surround signal is naturally present in virtually all of the current source material. This demonstrates the obviousness of the simple combination of the two systems. Other prior art matrix systems have offered six output channels, which included a center surround output. One prior art system is disclosed in U.S. Pat. No. 4,589,129 and also in U.S. Pat. No. 4,680,796 both issued to David E. Blackmer and James H. Townsend. Still another example of a matrix system offering a center surround output is disclosed in U.S. Pat. No. 5,172,415 issued to James W. Fosgate.
These prior art examples did not produce the level of separation that is obtained from the present invention, and in the Blackmer system there was no steering in the surround channels, which is required to enhance channel separation. The Blackmer system simply produced a pseudo stereo output for the left and right surround outputs, and an unaltered center surround output. The above examples illustrate the ongoing desire to increase the number of output channels in a surround system in order to improve localization and increase realism.
A relatively new matrix system, which has become commercially available in the past few years is a system called Circle Surround. The Circle Surround system is a 5-2-5 matrix system allowing five channels to be encoded down to two and then decoded back to five channels. The Circle Surround 5-2-5 matrix system is disclosed in U.S. Pat. No. 5,771,295 issued to James K. Waller Jr. The benefits of the 5-2-5 system over that of the Dolby Pro-Logic 4-2-4 matrix are clearly disclosed in the Waller patent. The advantages of combining the Circle Surround 5-2-5 matrix system with a discrete multi-channel audio system will become apparent after reading the disclosure of the current invention. In summary, the prior art systems lack the ability to provide more than one additional center surround channel and did not anticipate additional side or overhead channels. The prior art systems provided the additional center channel as an L+R signal that was naturally present as the summation of the two original channels. The prior art systems also did not anticipate the possibility of stereo encoded Lxe2x88x92R channels, or symmetrically encoded channels.
The present invention discloses an improved, expanded, combined discrete multi-channel/5-2-5 matrix system and the benefits of said system. It is an object of the current invention to offer additional channel enhancement to that available with the prior art systems by enhancing a multi-channel discrete system with 5-2-5 matrix encoded audio, mixed into at least two of the available discrete audio channels. It is a further object of the invention to offer the possibility of symmetrical channel enhancement. By encoding 5-2-5 matrix audio into any two of the five channels available, with Dolby Digital and DTS (Digital Theater Systems), or seven channels available with the Sony SDDS system, and then decoding with a Circle Surround decoder, the benefits of the invention are realized. As previously mentioned, the invention can also be used with the multi-channel discrete DVD audio format, which offers multiple discrete channels of audio. It is a further object of the invention to allow adjacent and or diagonal discrete channels to be used for additional matrix encoded channels. It is yet a further object of the invention to provide additional channel separation over that of the current Circle Surround system. The requirements of the stand alone system differ from that of the disclosed invention, and further improvements in performance are derived by providing surround channel attenuation when there is no dominate Lxe2x88x92R signal present. This will be further explained in the detailed description of the invention.
In the first embodiment of the invention a 5-2-5 matrix system is added to the surround channels of a discrete digital surround system providing an additional center surround channel and a pair of additional Lxe2x88x92R channels. The additional Lxe2x88x92R channels can be used for either overhead or side channels.
In a second embodiment of the present invention a multi-channel system is disclosed that offers symmetrical side and overhead channels to be added as L+R and Lxe2x88x92R channels.
In a third embodiment of the present invention a multi-channel system is disclosed that combines both of the first two embodiments with additional channels provided by encoding L+R signals and or Lxe2x88x92R signals in the front two audio channels.
The third embodiment provides for a total of up to fourteen available and independently addressable channels. As previously stated further improvements in the system performance are also achieved by reducing the gain in the surround channels of the 5-2-5 decoder when there is no dominate Lxe2x88x92R information present in the input audio.